1. Field of the Invention
The present invention relates to an image processing apparatus and, more particularly, to an image processing apparatus in which an analog-digital converted image signal is compressed and transmitted through a transmission medium or recording medium and, after that, the data is expanded and is digital-analog converted, and the image signal is generated.
2. Related Background Art
There is considered an image processing apparatus in which an image signal is divided into blocks each comprising a plurality of blocks and the data is orthogonal converted and the orthogonal converted data is quantized and variable length encoded so as to obtain a code amount in a certain range in said plurality of blocks.
As a method of selecting the plurality of blocks in such an image processing apparatus, a method as shown in FIGS. 1A and 1B is considered. FIG. 1A shows a whole image which is divided into (i=1 to n) blocks in the lateral direction and (j=1 to m) blocks in the vertical direction. Further, FIG. 1B shows one of the blocks divided in FIG. 1A and each block is further divided into (k=1 to l) blocks.
In the conventional image processing apparatus, the image signal is divided into blocks which is subjected to the orthogonal conversion as mentioned above. FIG. 2 shows a method of selecting (x) blocks in the case where the number of blocks is equal to x (x is an integer times as large as n) and they are x-block fixed length encoded.
In this instance, the value of (i) in FIG. 1A is sequentially increased from 1 to (n) and the value of (j) is properly changed within an x-block fixed length encoding. The value of (k) can be set to either the same value or different value.
For example, FIG. 3A shows a method of selecting every block when x=2n. FIG. 3B shows a method when x=4n. In FIGS. 3A and 3B, (t) indicates a time and the next block when t=1 is selected assumes t=2.
The image processing apparatus is constructed so as to select the block of the x-block fixed length encoding as mentioned above.
In the above conventional image processing apparatus, however, the Xth block in the x blocks which is subjected to the x-block fixed length encoding has a correlation for the horizontal direction of the image.
In the case where an error occurs in the Xth block in the x blocks, the blocks after the Xth block cannot be decoded and there are characteristics such that an error amount increases as the block approaches the end of the x-block fixed length encoding.
From the above description, there is a drawback such that the number of errors which occur gradually increases for the horizontal direction of the image and it becomes visually unsightly.
It is an object of the present invention to make it inconspicuous on a decoded image on a screen even if an error occurs during the image process in consideration of the above problems.
According to an embodiment of the invention, there is provided an image processing apparatus in which an image signal is divided into blocks each comprising a plurality of pixels and a quantization and a variable length encoding are executed so that a code amount of the plurality of blocks lies within a certain range, wherein the position of the block which is selected at the nth order among the plurality of blocks approaches to the periphery of the screen as the value of (n) increases.
Since the image processing apparatus of the embodiment is constructed by the above technical means, when the x-block fixed length encoding is performed, the block near the periphery of the screen is selected as an Xth block with an increase in value of (X). Therefore, even when an error occurs during the image process, the location of the error upon decoding relatively approaches the periphery of the image, so that the error is visually inconspicuous.
According to another embodiment of the invention, there is provided an image processing apparatus in which an image signal is divided into blocks each comprising a plurality of pixels and data of the plurality of divided blocks is orthogonal converted and the orthogonal converted data is quantized and variable length encoded so as to obtain a code amount in a certain range by a plurality of blocks, wherein those plurality of blocks don""t have any correlation in the vertical and horizontal directions of the image.
According to still another embodiment of the invention, when the above blocks are selected, by rotating the position to start the selection, the position of the block which is selected at the nth order in each of the plurality of blocks doesn""t have any correlation in the vertical and horizontal directions of the image.
Since the image processing apparatus of the embodiment is constructed by the above technical means, when the x-block fixed length encoding is performed, by selecting the Xth block so as not to have any correlation for the horizontal direction of the image, even if an error occurs during the image process, the location of the error is not concentrated to a predetermined portion for the horizontal direction of the image upon decoding.
Other objects and advantages of the present invention will become apparent from the following detailed description when taken in conjunction with the appended claims and the accompanying drawings.